Enucleation or evisceration of the eye is performed because of disease or trauma that make the removal of the eye, or the intraocular contents of the eye, necessary. Following such a procedure, the patient normally desires use of an artificial eye to restore a more normal appearance. To satisfactorily fit an artificial eye into the orbital socket, an orbital (herein also called an “ocular”) implant must be placed within the orbit to replace the volume that was lost when the eye or its contents was removed. However, the use of an orbital implant and the subsequent fitting of the artificial eye confer more than a cosmetic benefit. They help maintain the normal structure of the eyelids and eyebrows; they aid in normal tear drainage; and, when used in children, they help stimulate normal growth of the orbital bones.
It is further known that such treatment is enhanced by encouraging fibrovascular ingrowth into porous implants so that they may become integrated as disclosed in Perry, U.S. Pat. No. 6,063,117 incorporated herein by this reference.
Porous materials such as hydroxyapatite (“HA”) do have some drawbacks. Naturally derived HA exhibits surface spicules which can abrasively contact other structures within the orbit which can make insertion difficult. Further abrasion can occur after insertion, leading to the generally unwanted condition of exposure of the implant.
It has been found that a coating or wrapping of a smooth, sheet material on the outer surface of the porous core of the implant can provide a smooth surface which will facilitate deep insertion. The coating also provides a secure structure onto which the extraocular muscles may be sutured in close proximity to the implant in order to provide a good blood supply for encouraging rapid fibrovascular ingrowth. Unfortunately, such a coating can discourage rapid fibrovascular ingrowth by blocking access of bodily fluids and blood vessels to the porous core. Additionally, simply wrapping the hydroxyapatite core with such a material may present additional preparatory steps to the surgeon such that the muscle attachments may be readily affixed to the covering material and into intimate contact with the core.
It is further shown in Perry, U.S. Pat. No. 6,248,130, incorporated herein by this reference, that a coating made of bioabsorbable sheet material will allow both easy insertion and, as it degrades, allow full integration with fibrovascular tissue. The materials selected for the coating should not cause an undue adverse immune or inflammatory response and, preferably, will be rapidly bioabsorbed or penetrated by the patient's body to allow integration with fibrovascular tissue. Preferably, the coating must be made from a material which is strong enough to securely hold sutures.
Various materials have been proposed from plaster of paris to biodegradable polymeric compounds such as polyglycolic acid (“PGA”), and polylactic acid (“PLA”) among others. Depending on various parameters such as its molecular morphology (crystalline vs. amorphous), hydrophobicity, and presence of additives, among others, such materials typically exhibit different rates of degradation in the body and will become bio-absorbed at different times.
This required manufacturers to weigh the benefits of a faster degrading coating which would encourage more rapid vascularization against the disadvantages of less secure muscle attachment over time, and the irritation caused by projecting spicules. Although slower degradation provides longer lasting smoothness, secure muscle attachment, and encourages epithelial cell growth if exposed, it discourages rapid fibrovascular ingrowth.
There is a need, therefore, to provide an implant that minimizes the above-described negative effects.